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lib/ts_kmp: fix integer overflow in pattern length calculation

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The ts_kmp algorithm stores its prefix_tbl[] table and pattern in a single
allocation sized from the pattern length.  If the prefix_tbl[] size
calculation wraps, the resulting allocation can be too small and
subsequent pattern copies can overflow it.

Fix this by rejecting zero-length patterns and by using overflow helpers
before calculating the combined allocation size.


This fixes a potential heap overflow.  The pattern length calculation can
wrap during a size_t addition, leading to an undersized allocation. 
Because the textsearch library is reachable from userspace via Netfilter's
xt_string module, this is a security risk that should be backported to LTS
kernels.

Link: https://lkml.kernel.org/r/20260308202028.2889285-2-objecting@objecting.org
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Josh Law
2026-03-08 20:20:28 +00:00
committed by Andrew Morton
parent 9003ec6f7f
commit 8cdf30813e
1 changed files with 16 additions and 2 deletions
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18
lib/ts_kmp.c
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@@ -94,8 +94,22 @@ static struct ts_config *kmp_init(const void *pattern, unsigned int len,
struct ts_config *conf;
struct ts_kmp *kmp;
int i;
unsigned int prefix_tbl_len = len * sizeof(unsigned int);
size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;
unsigned int prefix_tbl_len;
size_t priv_size;
/* Zero-length patterns would make kmp_find() read beyond kmp->pattern. */
if (unlikely(!len))
return ERR_PTR(-EINVAL);
/*
* kmp->pattern is stored immediately after the prefix_tbl[] table.
* Reject lengths that would wrap while sizing either region.
*/
if (unlikely(check_mul_overflow(len, sizeof(*kmp->prefix_tbl),
&prefix_tbl_len) ||
check_add_overflow(sizeof(*kmp), (size_t)len, &priv_size) ||
check_add_overflow(priv_size, prefix_tbl_len, &priv_size)))
return ERR_PTR(-EINVAL);
conf = alloc_ts_config(priv_size, gfp_mask);
if (IS_ERR(conf))